If a ghost bus is a bus that appears in a bus app but doesn't exist on the road, then we could call a bus that isn't in the app but does exist on the road an antighost bus. I just travelled one.
I'm standing at a stop for northbound bus 76 in Bristol. A 76 that is not shown as expected at that stop on bustimes.org turns up. I know it's not shown as expected because bustimes.org gives the actual licence plate number (let's say 1234 XYZ), so I can see that this license plate was not on the list of expected buses. I get on. The first thing I check is that bus 1234 XYZ is showing as a live bus on the bustimes.org route map, and yes it is. Even though it was not shown on the expected list, it is on the route map and there is its little icon pootling merrily up Gloucester Road with my GPS next to it.
Then, I look if it is shown as an expected bus at the next stop. No it's not. It's on the road, it's on the route map, but it's not on the expected list for the next stop. It's also not on the expected list at the second stop ahead, the third, or fourth or fifth. But it IS shown as expected at the sixth and seventh stops ahead. And when I check back at stops 2, 3, 4, 5, it is still not shown on those, so it's not like it's appeared on all stops everywhere all at once.
An explanation would be if it was terribly late and the system had given up on it and thought it had already passed stops 2 - 5 ahead. But bustimes.org reports how late/early each bus is, and this one is not shown as late.
So the bus is real but it is shown as an expected bus on some but not all stops on the route ahead of it. Am I right to be puzzled - am I missing something simple? What's going on?